import {settings} from "../settings"

export function startsWith(str: string, searchString: string, position: number = 0): boolean {
  return str.substr(position, searchString.length) == searchString
}

export function uuid4(): string {
  // from ipython project
  // http://www.ietf.org/rfc/rfc4122.txt
  const s = new Array<string>(32)
  const hexDigits = "0123456789ABCDEF"
  for (let i = 0; i < 32; i++) {
    s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1)
  }
  s[12] = "4"                                                     // bits 12-15 of the time_hi_and_version field to 0010
  s[16] = hexDigits.substr((s[16].charCodeAt(0) & 0x3) | 0x8, 1)  // bits 6-7 of the clock_seq_hi_and_reserved to 01

  return s.join("")
}

let counter = 1000

export function uniqueId(prefix?: string): string {
  const id = settings.dev ? `j${counter++}` : uuid4()

  if (prefix != null)
    return `${prefix}-${id}`
  else
    return id
}

export function escape(s: string): string {
  return s.replace(/(?:[&<>"'`])/g, (ch) => {
    switch (ch) {
      case '&': return '&amp;'
      case '<': return '&lt;'
      case '>': return '&gt;'
      case '"': return '&quot;'
      case "'": return '&#x27;'
      case '`': return '&#x60;'
      default:  return ch
    }
  })
}

export function unescape(s: string): string {
  return s.replace(/&(amp|lt|gt|quot|#x27|#x60);/g, (_, entity) => {
    switch (entity) {
      case 'amp':  return '&'
      case 'lt':   return '<'
      case 'gt':   return '>'
      case 'quot': return '"'
      case '#x27': return "'"
      case '#x60': return '`'
      default:     return entity
    }
  })
}

export function use_strict(code: string): string {
  return `'use strict';\n${code}`
}
